U.S. patent application number 11/843814 was filed with the patent office on 2009-02-26 for rechargeable air battery and manufacturing method.
Invention is credited to Lonnie G. Johnson, Prabhakar A. Tamirisa, Ji-Guang Zhang.
Application Number | 20090053594 11/843814 |
Document ID | / |
Family ID | 40382488 |
Filed Date | 2009-02-26 |
United States Patent
Application |
20090053594 |
Kind Code |
A1 |
Johnson; Lonnie G. ; et
al. |
February 26, 2009 |
RECHARGEABLE AIR BATTERY AND MANUFACTURING METHOD
Abstract
An air battery having an air cathode having a porous carbon
based air cathode containing a non-aqueous organic solvent based
electrolyte including a lithium salt and an alkylene carbonage
additive. The battery also includes a separator loaded with an
organic solvent based electrolyte including a lithium salt and an
alkylene carbonate additive, a cathode current collector, an anode,
an anode current collector, and a housing. The housing contains the
cathode, separator, cathode current collector, anode, anode current
collector, and a supply of air.
Inventors: |
Johnson; Lonnie G.;
(Atlanta, GA) ; Tamirisa; Prabhakar A.; (Atlanta,
GA) ; Zhang; Ji-Guang; (Richland, WA) |
Correspondence
Address: |
BAKER, DONELSON, BEARMAN, CALDWELL & BERKOWITZ;Intellectual Property
Department
Monarch Plaza, Suite 1600, 3414 Peachtree Rd.
ATLANTA
GA
30326
US
|
Family ID: |
40382488 |
Appl. No.: |
11/843814 |
Filed: |
August 23, 2007 |
Current U.S.
Class: |
429/163 |
Current CPC
Class: |
H01M 4/133 20130101;
H01M 4/131 20130101; H01M 4/587 20130101; H01M 4/90 20130101; Y02E
60/10 20130101; H01M 10/0568 20130101; H01M 10/052 20130101; Y02E
60/128 20130101; H01M 10/0567 20130101; H01M 12/08 20130101 |
Class at
Publication: |
429/163 |
International
Class: |
H01M 2/02 20060101
H01M002/02 |
Claims
1. An air battery comprising: an air cathode; a separator loaded
with an organic solvent based electrolyte including a lithium salt
and an alkylene carbonate additive; a cathode current collector; an
anode; an anode current collector; and a housing containing said
cathode, said separator, said cathode current collectors said
anode, said anode current collector, and a supply of air.
2. The air battery of claim 1 wherein said separator is a polymeric
material.
3. The air battery of claim 2 wherein said separator is a porous
polymeric material.
4. The air battery of claim 1 wherein said air cathode is loaded
with an oxygen reduction catalyst.
5. The air battery of claim 4 wherein said oxygen reduction
catalyst is selected from the group consisting of electrolytic
manganese dioxide, ruthenium oxide, silver, platinum and
iridium.
6. The air battery of claim 1 wherein said lithium salt is selected
from the group consisting of lithium hexafluorophosphate, lithium
tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate,
lithium bis(trifluorosulfonyl) imide, lithium triflate, lithium
bis(oxalato) borate, lithium tris(pentafluoroethyl)
trifluorophosphate, Lithium bromide, and lithium iodide.
7. The air battery of claim 1 wherein said alkylene carbonate
additive is selected from the group consisting of vinylene
carbonate and butylene carbonate.
8. The air battery of claim 4 wherein the concentration of oxygen
reduction catalyst is between 1% and 30% by weight.
9. The air battery of claim 1 wherein said cathode is a carbon
based air cathode containing a non-aqueous organic solvent based
electrolyte including a lithium salt and an alkylene carbonate
additive.
10. The air battery of claim 1 wherein said anode is selected from
the group consisting of lithium metal, lithium metal based alloys,
and lithium intercalation compounds.
11. The air battery of claim 1 wherein said anode is selected from
the group consisting of graphite, MCMB graphite, soft carbon and
lithium titanate.
12. An air battery cathode comprising porous carbon based air
cathode containing a non-aqueous organic solvent based electrolyte
including a lithium salt and an alkylene carbonate additive.
13. The air battery cathode of claim 12 wherein said alkylene
carbonate additive is selected from the group consisting of
vinylene carbonate and butylene carbonate.
14. The air battery cathode of claim 12 wherein said lithium salt
is selected from the group consisting of lithium
hexafluorophosphate, lithium tetrafluoroborate, lithium
hexafluoroarsenate, lithium perchlorate, lithium
bis(trifluorosulfonyl) imide, lithium triflate, lithium
bis(oxalato) borate, lithium tris(pentafluoroethyl)
trifluorophosphate, Lithium bromide, and lithium iodide.
15. The air battery cathode of claim 14 wherein said alkylene
carbonate additive is selected from the group consisting of
vinylene carbonate and butylene carbonate.
16. An air battery comprising: an air cathode having a porous
carbon based air cathode containing a non-aqueous organic solvent
based electrolyte including a lithium salt and an alkylene
carbonage additive; a separator loaded with an organic solvent
based electrolyte including a lithium salt and an alkylene
carbonate additive; a cathode current collector; an anode; an anode
current collector; and a housing containing said cathode, said
separator, said cathode current collector, said anode, said anode
current collector, and a supply of air.
17. The air battery of claim 16 wherein said separator is a
polymeric material.
18. The air battery of claim 16 wherein said air cathode includes
an oxygen reduction catalyst.
19. The air battery of claim 16 wherein said air cathode is loaded
with an oxygen reduction catalyst.
20. The air battery of claim 19 wherein said oxygen reduction
catalyst is selected from the group consisting of electrolytic
manganese dioxide, ruthenium oxide, silver, platinum and
iridium.
21. The air battery of claim 16 wherein said cathode lithium salt
and said separator lithium salt are lithium
hexafluorophosphate.
22. The air battery of claim 16 wherein said cathode lithium salt
and said separator lithium salt are selected from the group
consisting of lithium hexafluorophosphate, lithium
tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate,
lithium bis(trifluorosulfonyl) imide, lithium triflate, lithium
bis(oxalato) borate, lithium tris(pentafluoroethyl)
trifluorophosphate, Lithium bromide, and lithium iodide.
23. The air battery of claim 16 wherein said cathode alkylene
carbonate additive and said separator alkylene carbonate additive
are selected from the group consisting of vinylene carbonate and
butylene carbonate.
24. The air battery of claim 18 wherein said oxygen reduction
catalyst is selected from the group consisting of electrolytic
manganese dioxide, ruthenium oxide, silver, platinum and
iridium.
25. The air battery of claim 16 wherein said anode is selected from
the group consisting of lithium metal, lithium metal based alloys,
and lithium intercalation compounds.
26. The air battery of claim 16 wherein said anode is selected from
the group consisting of graphite, MCMB graphite, soft carbon and
lithium titanate.
Description
TECHNICAL FIELD
[0001] This invention relates generally to batteries, and more
particularly to air cathode type batteries.
BACKGROUND OF THE INVENTION
[0002] Lithium-air batteries consist of lithium anodes
electrochemically coupled to atmospheric oxygen through an air
cathode. Oxygen gas introduced into the battery through an air
cathode is essentially an unlimited cathode reactant source. These
batteries have a very high specific energy and a relatively flat
discharge voltage profile. A problem with present air batteries is
their limited rechargeability.
[0003] It would be beneficial to provide an lithium-air battery
that is rechargeable and easier to manufacture than those of the
prior air. Accordingly, it is to the provision of such that the
present invention is primarily directed.
SUMMARY OF THE INVENTION
[0004] In a preferred form of the invention an air battery
comprising an air cathode having a porous carbon based air cathode
containing a non-aqueous organic solvent based electrolyte
including a lithium salt and an alkylene carbonage additive. The
battery also includes a separator loaded with an organic solvent
based electrolyte including a lithium salt and an alkylene
carbonate additive, a cathode current collector, an anode, an anode
current collector, and a housing. The housing contains the cathode,
separator, cathode current collector, anode, anode current
collector, and a supply of air.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1(a) is a schematic diagram of an air battery embodying
principles of the invention in a preferred form.
[0006] FIG. 1(b) is a schematic diagram of an air battery embodying
principles of the invention in another preferred form.
[0007] FIG. 1(c) is a schematic diagram of an air battery embodying
principles of the invention in yet another preferred form.
[0008] FIG. 2 is a schematic diagram of a double cell
structure.
[0009] FIG. 3(a)3(c) are a series of sequential views of the
battery manufacturing method.
[0010] FIG. 4 is a chart showing the charge/discharge behavior of
the air battery of the present invention.
[0011] FIG. 5 is a chart showing the charge/discharge cycling of
the air battery of the present invention.
[0012] FIG. 6 is a chart showing the cycling stability of the air
battery of the present invention.
[0013] FIG. 7 is a chart showing the voltage/current profile of the
air battery of the present invention.
[0014] FIG. 8 is a chart showing the cyclability of the air battery
of the present invention.
[0015] FIG. 9 is a chart showing the cycling stability of the air
battery of the present invention.
[0016] FIG. 10 is a chart showing the cyclic voltammetry of the air
battery of the present invention.
[0017] FIG. 11 is a chart showing the cyclic voltammetry of the air
battery of the present invention.
[0018] FIG. 12 is a chart showing the cyclic voltametry of the air
battery of the present invention.
[0019] FIG. 13 is a chart showing the voltage/current profiles and
cycling stability of the air battery of the present invention.
[0020] FIG. 14 is a chart showing the voltage/current profiles of
the air battery of the present invention.
[0021] FIG. 15 is a chart showing the cycling behavior of the air
battery of the present invention.
[0022] FIG. 16 is a chart showing the cycling stability of the air
battery of the present invention.
[0023] FIG. 17 is a chart showing the voltage/current profiles of
the air battery of the present invention.
[0024] FIG. 18 is a chart showing the cycle stability of the air
battery of the present invention.
[0025] FIG. 19 is a chart showing the voltage/current profiles and
cycling behavior of the air battery of the present invention.
DETAILED DESCRIPTION
[0026] With reference next to the drawings, there is shown in a
battery or electrochemical cell 10 and method of producing such
embodying principles of the invention in a preferred form. The cell
10 includes an air cathode 11, a cathode current collector 12, a
separator 13, an anode 14, and an anode current collector 15.
[0027] To produce the cell 10 a Teflon bonded, Calgon carbon
(activated carbon) based air cathode 11 is prepared by first
wetting 14.22 g of Calgon carbon, 0.56 g of Acetylene black, and
0.38 g of electrolytic manganese dioxide by a 60 ml mixture of
Isopropanol and water (1:2 weight ratio). The electrolytic
manganese dioxide is an oxygen reduction catalyst, preferably
provided in a concentration of 1% to 30% by weight. Alternatives to
the electrolytic manganese dioxide are ruthenium oxide, silver,
platinum and iridium. Next, 2.92 g of Teflon 30 (60% Teflon
emulsion in water) is added to the above mixture, mixed, and placed
in a bottle with ceramic balls to mix overnight on the rollers.
After mixing, the slurry/paste is dried in an oven at 110.degree.
C. for at least 6 hours to evaporate the water, and obtain a dry,
fibrous mixture. The dry mixture is then once again wetted by a
small quantity of water to form a thick paste, which is then spread
over a clean glass plate. The mixture is kneaded to the desired
thickness as it drys on the glass plate. After drying, it is cold
pressed on an Adcote coated Aluminum mesh at 4000 psi for 3
minutes. To remove any cracks in the paste, the cathode assembly is
passed through stainless steel rollers. The cathode is then cut
into smaller pieces such that the active area of the cathode is 2''
by 2''. A small portion of the aluminum mesh is exposed so that it
may be used as the current collector tab.
[0028] The cell assembly is performed inside of an argon filled
glove box. The cathode is wet by a non-aqueous organic solvent
based electrolyte including a lithium salt and an alkylene
carbonate additive. The electrolyte may be lithium
hexaflouraphosphate (1 M LiPF.sub.6 in PC:DME). A pressure
sensitive porous polymeric separator membrane (Policell, type B38)
is placed on the cathode, with the shiny side facing away from the
cathode. Next, a thin Li foil is placed on the wet separator, and a
1.5 cm.times.4 cm strip of copper mesh is placed along one edge,
away from the aluminum mesh tab. Another cathode piece wet by the
electrolyte and covered with the separator is placed directly on
top of the lithium foil, and copper mesh strip. The double cell
structure is shown in FIG. 2. This assembly is laminated on a hot
press at 100.degree. C., and 500 lb for 30-40 seconds. After the
sample is withdrawn from the press, the heat activated separator
binds the sample together. It should be understood that the
separator is loaded with an organic solvent based electrolyte
including a lithium salt and an alkylene carbonate such as vinylene
carbonate or butylene carbonate.
[0029] A bag made of multilayer polymer/metal lamination is
pre-sealed on three sides, and has one side partially open as shown
in FIG. 3(a). On the fourth, partially open side, a syringe needle
is sealed into the bag. The top of the needle is sealed with epoxy.
In addition, a partial seam is created along the length of the
needle so the bag can be easily sealed. After ensuring that the
cathode is not peeling from the separator, the assembly is soaked
in the electrolyte for at least 5-10 minutes, and then inserted
into the pre-assembled `blue bag` pouch and sealed across the
current collector mesh tabs (see FIG. 3(b). The pouch battery is
then removed from the glove box and a syringe is used to inject
oxygen through an epoxy filled fine tube. After injecting oxygen,
the pouch is sealed once again, closer to the electrode assembly,
using an impulse sealer, and the syringe-containing portion of the
blue bag is trimmed, as shown in FIG. 3(c).
[0030] Previous reports showed reversibility of Li/O.sub.2 battery
only up to 3-4 cycles at low current densities. In a recently
published paper, Ogasawara et al, J. Am. Chem. Soc. Vol. 128, 1390
(2006) reported that Li.sub.2O.sub.2 can be electrochemically
decomposed to lithium and O.sub.2 by charging to 4.5 V. However, no
distinction was made between Li.sub.2O.sub.2 and Li.sub.2O, and no
information was provided on the reversibility of Li.sub.2O. To
decompose Li.sub.2O.sub.2 formed during the discharge cycle, it is
necessary to charge the cell to >4 V vs. Li.sup.+/Li. Indeed,
charge capacity of the Li/O.sub.2 cells at a voltage .ltoreq.3.9 V
vs. Li.sup.+/Li was very limited. Several experiments were
conducted to check for reversibility when cells were charged to
>4.0 V vs. Li.sup.+/Li. When the cells were charged to >4.0
V, significant amounts of mossy lithium metal deposits were found
on the anode at the end of almost all experiments, suggesting that
lithium metal is being plated on the anode during charging. In the
first experiment, a carbon cathode (72.6% Calgon carbon/3% carbon
black/4.4% MnO.sub.2, 20% Teflon) with nickel mesh current
collector was used in a cell consisting of a lithium metal foil as
anode, and 1 M LiPF.sub.6 in EC:DEC (1:1) as electrolyte. The cell
was discharged to 2.3 V at 0.4 mA/cm.sup.2, and charged to 4.3 V at
the same current density; charge and discharge were terminated when
the current reached 0.2 mA/cm.sup.2 at constant voltage (FIG. 4).
After three cycles, the width of the discharge plateau decreased,
and the cell capacity dropped to .about.1 mAh (FIG. 5). Reducing
the low voltage limit from 2.3 V to 2 V during the last cycle
resulted in a large increase in the battery capacity, but this
increased capacity diminished in the next cycle.
[0031] The effect of cathode additive (lithium peroxide, lithium
oxide, or lithium superoxide) (Li.sub.2O.sub.2 or Li.sub.2O) on
Li/O.sub.2 batteries has been investigated extensively. The
composition of a typical Li.sub.2O.sub.2 containing cathode with
the weight ratios of the various components in the cathode are as
the following: Calgon carbon (71.1%), Li.sub.2O.sub.2 (14%),
electrolytic MnO.sub.2 (EMD) (1.9%), Kynar (10.2%), and carbon
black (2.8%). First, 0.8 g of Kynar.RTM. (Elf Atochem North
America, Inc.) was heat-dissolved (at 50.degree. C.) in 20 ml
acetone with active stirring, and then 5.6 g of carbon powder
(Calgon, PWA), 1.1 g of Li.sub.2O.sub.2, 0.15 g of electrolytic
manganese dioxide (EMD) (catalyst), and 0.22 g of carbon black were
added and stirred overnight. The gel-like paste was cast on glass
and acetone was allowed to evaporate. The thickness of the cast was
.about.0.2 mm. The cast film (before it is fully dried) was placed
on nickel mesh (cleaned in 5% NaOH for 30 seconds, washed by
isopropyl and then dried in 80.degree. C. oven) and laminated
between two Kapton sheets using a stainless roller. Finally, the
sample was dried in an 80.degree. C. oven overnight. The final
thickness of the air electrode was .about.0.1 mm thick. The sample
area was 1 cm.sup.2. The unit weight (g/cm.sup.2) of mesh and
sample/mesh were weighed to calculate the sample weight.
Alternatively, the gel-like paste may be cast directly on expanded
metal mesh, and calendared.
[0032] Charge/discharge cycles were performed at constant current
of 0.5 mA/cm.sup.2 between 4.5 V and 2.3 V; the cut off current
during constant voltage charge/discharge was 0.1 mA/cm.sup.2. The
charge/discharge profile and cycling capacity of the cell is shown
in FIG. 6. One of the reasons for the cycle fade may be the
formation of discharge products such as Li.sub.2O which may not be
decomposed during the charge process. In fact, Read (Journal of The
Electrochemical Society, 149-9, A1190, 2002) reported that 67% of
the discharge product was Li.sub.2O.sub.2, the rest was Li.sub.2O
when the same electrolyte (1 M LiPF.sub.6 in PC) was used.
Apparently, a better electrolyte is required to produce more
reversible Li.sub.2O.sub.2 as the discharge product.
[0033] Ogasawara et al. indicated that it is possible to decompose
Li.sub.2O.sub.2 by charging to more than 4.3 V in a PC-based
electrolyte. On the other hand, there is no concrete evidence to
demonstrate the reversibility of Li.sub.2O. Therefore, to insure
the rechargeability of Li/O.sub.2 battery, it is prudent to
preferentially form Li.sub.2O.sub.2 (instead of Li.sub.2O) during
discharge process. Read indicated that composition of the discharge
by-product strongly depends on the selection of electrolyte. Table
2 lists the percentage of Li.sub.2O.sub.2 and Li.sub.2O formed
during the discharge process when different electrolyte is used in
Li/O.sub.2 cells. The table indicates that 1M LiPF.sub.6 in PC:DME
(1:1) or 1 M LiPF.sub.6 in PC:THF (1:1) are good candidates because
these electrolytes lead to almost 100% production of
Li.sub.2O.sub.2 instead of Li.sub.2O in the discharge process.
[0034] In addition to electrolyte formulation, lower discharge
rates, and higher oxygen concentrations in the electrolyte also
favored the formation of Li.sub.2O.sub.2 instead of Li.sub.2O.
Furthermore, oxygen concentration in the electrolyte is determined
by the solubility of oxygen in the electrolyte. Since ether based
solvents have the highest oxygen solubilities among the organic
solvents used in lithium batteries, low discharge rates in
ether-based solvents are likely to form Li.sub.2O.sub.2
preferentially. This is consistent with the preferential formation
of Li.sub.2O.sub.2 in PC:DME and PC:THF electrolyte as shown in
Table 2. Since higher charge voltages are likely to completely
charge the cell, and EC:DEC electrolyte itself may decompose when
charged to >4.3 V, initially, a different cell using 1 M
LiPF.sub.6 in PC was used to access the higher voltages. In this
cell, a Li.sub.2O.sub.2 containing cathode was used in conjunction
with a lithium metal foil anode.
[0035] Several cells with ether-based solvents have been prepared.
The cells tested in electrolyte containing THF is unstable at
higher voltages (>4V). Read showed that 97% of the discharge
products in Li/O.sub.2 cells using PC:DME based electrolyte was
Li.sub.2O.sub.2. Therefore, this electrolyte has been used in the
subsequent investigation. FIG. 7 shows the charge/discharge
profiles of a Li/O.sub.2 cell with a carbon cathode containing 14%
Li.sub.2O.sub.2, a lithium metal foil anode, and 1 M LiPF.sub.6 in
PC:DME (1:2) as the electrolyte. The discharge capacity of the cell
increased to more than 14 mAh which is much higher than the sample
with no Li.sub.2O.sub.2 premixed in cathode. The cell also
demonstrates significant rechargeability as shown in FIG. 8. The
capacity fade is 5.4%/cycle during the first 15 cycles.
[0036] To examine the effect of the calendaring, another cathode
was prepared by injecting the diluted cathode slurry into the
cathode space confined by a Teflon holder. The cathode consists of
a slurry of Calgon carbon, carbon black, Li.sub.2O.sub.2, and
Electrolytic MnO.sub.2, but it did not contain any binder (usually
Kynar). The cathode was not calendared before use. Two drops of the
powders mixed in the electrolyte (PC:DME (1:2)) were placed on an
Al mesh current collector, and the cell was subjected to
charge/discharge cycling. The sample was cycled between 2.3 to
4.3V. Cycling stability of this Li/O.sub.2 cell are shown in FIG.
9. While the second cell with the liquid slurry cathode seemed to
perform well in the first few cycles with relatively less capacity
fade, the fade increased in the latter cycles, which also resulted
in the loss of the characteristic discharge profiles with two
inflection points. After 13 cycles, both cells show the similar
capacity fade (.about.5.4%/cycle).
[0037] While the progress in developing reversible Li/O.sub.2
batteries has been encouraging, several issues remain to be solved.
One of the main concerns is on the origin of the rechargeability.
Although Ogasawara verified the decomposition of Li.sub.2O.sub.2
(during charge process) by mass spectrometry, other mechanisms may
also contribute to the charge capacity. These mechanisms include
decomposition of electrolyte (which is strongly affected by
solvent, cathode, catalyst, and current collector) and other side
effects. The capacity fade during cycling is also directly related
to the charging mechanism.
[0038] As we can see from the test data shown in this report, the
discharge plateau shrinks with increasing number of cycles,
suggesting that the cell reactions may not be completely reversed
during charging after prolonged cycling. One of the major reasons
for this behavior may be the formation of small amounts of
Li.sub.2O during discharge, which, unlike Li.sub.2O.sub.2, may not
be easily decomposed during charging. As the "irreversible"
Li.sub.2O formed in each discharge blocks the pores of the carbon
cathode during discharge, the capacity of the carbon cathode for
subsequent discharge cycles is reduced; hence some capacity fade
may be inevitable.
[0039] To identify the charging mechanism and source of capacity
fade in a Li/O.sub.2 cell, cyclic voltammetry has been used to
investigate the Li.sub.2O.sub.2 decomposition, and oxygen reduction
during charge and discharge processes. The cell used a lithium foil
anode, a Li.sub.2O.sub.2 containing cathode (with Al current
collector) and 1 M LiPF.sub.6 in PC:DME (1:2 by wt.) as
electrolyte. The cyclic voltammogram curves are shown in FIG. 10.
The sample was cycled between 2 and 4.9 V with a scan rate of 0.1
mV/s. A clear cathodic peak, corresponding to the reduction of
oxygen in the aprotic electrolyte has been identified at .about.2.7
V vs. Li.sup.+/Li and this peak moved to .about.2.5 V with
increasing cycle number. The current of the cathodic, oxygen peak
decreases with increased number of cycles; this decreased peak is
directly related to the cycle fade in the Li/O.sub.2 cell. Although
it is not very clear during the first two charge cycles, an anodic
peak at .about.4.6 V starts to appear during the third cycle. It is
interesting to note that the decreasing peak values during the
discharge cycles coincide with the decreasing peak values during
the charge cycles. Both phenomena are also consistent with the
capacity fade of the cell.
[0040] Another Li/O.sub.2 cell with the exactly same structure as
those shown in FIG. 11 has been cycled at a much slower rate (0.01
mV/s). The cyclic voltammetry data of this sample is shown in FIG.
11. The anodic current started to increase from .about.4.2 V and
peaked at 4.68 V, then started to decrease until 4.9V. The clear
peak at .about.4.6 V can be identified as the decomposition of the
lithium peroxide. The monotonic increase of anodic current after
4.9 V can be attributed to the decomposition of electrolyte. The
cyclic voltammetry data shown in this section has successfully
confirmed that the charge/discharge capacity shown in the cycling
data of Li/O.sub.2 cells process (see previous sections) is
directly related to a reversible electrochemical process, not to
the decomposition of electrolyte.
[0041] A similar test was conducted for a cathode containing 30%
Li.sub.2O.sub.2 to see if the anodic peak may be greater than the
one observed in previous experiments which used 14%
Li.sub.2O.sub.2. The cell has a composition of the following:
Calgon carbon (57%), Li.sub.2O.sub.2 (30%), Electrolytic MnO.sub.2
(EMD) (2%), Kynar (10%), and carbon black (3%). Al mesh was used as
the current collector; Li anode; 1 M LiPF6 in PC:DME (1:2) was used
as the electrolyte. The cyclic voltammetry data of the cell
(cv0212a.044) is shown in FIG. 10. The sample was cycled in 1 M
LiPF.sub.6 in PC:DME (1:2) at a rate of 0.1 mV/s. Comparing the
cyclic voltammetry data shown in FIG. 10 and FIG. 12, anodic peak
(at .about.4.6V) in the sample contain 30% Li.sub.2O.sub.2 (see
FIG. 12) is similar to those observed in the case of 14%
Li.sub.2O.sub.2 cathodes (see FIG. 10). This observation is the
further evidence that the anodic peaks at .about.4.6 V
corresponding to the decomposition of Li.sub.2O.sub.2.
[0042] Since anodic peaks at 4.6 V (which is assumed to be related
to decomposition of Li.sub.2O.sub.2) were found in cells that used
either PC:DME or PC based electrolytes, cells were set up for
charge/discharge cycling between 4.8 and 2.3 V. Further examination
of the test results show that significant current or voltage noise
were found during the initial stage of the charging process.
Therefore, a "formation" process has been introduced at the
beginning of the charge cycle to stabilize the samples. A stepwise
current profile was used during the first charging process to
facilitate the formation of possible solid electrolyte interface on
the carbon electrolyte. This formation process has been proved to
be very useful in noise reduction. The results from a Li/O.sub.2
cells with a cathode containing 14% Li.sub.2O.sub.2 and cycled in 1
M LiPF.sub.6 in PC:DME (1:2) are shown FIG. 13. During the initial
cycle, cell voltage started to drop when it reach 4.65V. This may
related to the exhaustion of Li.sub.2O.sub.2 pre-mixed in the
electrode. Further current flow after all of Li.sub.2O.sub.2 was
decomposed may related to the decomposition of electrolyte or
current collector corrosion.
[0043] The initial voltage drop shown in FIG. 11 may related to the
decomposition of electrolyte or corrosion of current collectors.
FIGS. 14 and 15 shows the voltage/current profiles and cycling
behavior of a Li/O.sub.2 cell, respectively, that includes vinylene
carbonate as an electrolyte additive. The sample was tested in an
electrolyte with Vinylene carbonate additive (1 M LiPF.sub.6 in
PC:DME with 2% Vinylene carbonate). Sample cathode has 14% of
Li.sub.2O.sub.2. The cell voltage showed a dip in the voltage at
constant current charging in the first cycle itself, and the cell
did not charge to >4.4 V. This may be related to the formation
of a solid electrolyte interface during the first cycle. The cell
exhibited good discharge profile, and capacity, and the second
charge cycle did not exhibit any noise.
[0044] FIG. 16 shows the cycling stability of another Li/O.sub.2
cell (La0417b.042) cycled in an electrolyte with Vinylene carbonate
additive (1 M LiPF.sub.6 in PC:DME with 2% Vinylene carbonate).
Sample cathode has 14% of Li.sub.2O.sub.2. An Al rod was used to
connect cathode current collector to the outside of the cell.
Excellent Coulomb efficiency has been observed on this sample.
[0045] FIG. 16 Cycling stability of another Li/O.sub.2 cell
(La0417b.042) tested in an electrolyte with Vinylene carbonate
additive (1 M LiPF.sub.6 in PC:DME with 2% Vinylene carbonate).
Sample cathode has 14% of Li.sub.2O.sub.2. Al rod was used to
connect cathode current collector to the outside of the cell.
[0046] Most of previous tests have used conventional CCCV (constant
current followed by constant voltage) procedures to test Li/O.sub.2
batteries. While there was significant improvement in the cycle
life by increasing the voltage limit for charging, the charging
profiles were always plagued with noise, especially in the voltage,
during constant current charging, and sometimes in the current
during constant voltage charging at the voltage limit. Attempts at
eliminating this noise by changing the electrolytes and current
collectors, and applying surface treatments to current collectors
resulted in mixed successes.
[0047] Recently, a different charging procedure has been adopted
for the Lithium-oxygen batteries. The new charging process relies
on an initial stage of constant current charging, however, charging
is terminated when the battery voltage drops by a value specified
in the charging routine (typically 20-50 mV). This charging
procedure, also referred to as a "negative .DELTA.V" charge control
procedure, is widely used in Nickel-Cadmium and Nickel-Metal
Hydride batteries, and allows termination of charge when the
battery voltage drops after reaching a peak voltage. In the case of
the Lithium-oxygen battery, the drop in the voltage is believed to
occur due to the completion of decomposition of Li.sub.2O.sub.2. In
fact, there is a good agreement between the values of charge
required for the negative .DELTA.V event on the first charge
process, and the theoretical value of charge required to decompose
the Li.sub.2O.sub.2 loaded in the cathode. In addition to the
negative .DELTA.V method of charge termination, a voltage limit of
4.7 V has been included in the charging algorithm, and a second
criterion of time has been included to terminate charge, if the
battery switches to constant voltage charging, after reaching the
voltage limit. In the future, a more elegant control, based on the
electrochemical signature of the completion of Li.sub.2O.sub.2
decomposition may be used.
[0048] For the Lithium-oxygen battery, the use of a negative
.DELTA.V method of charge control/termination seems to be more
appropriate than a CCCV process, because upon charging, unlike in a
traditional Li-ion battery, the decomposition products, Li and
oxygen gas do not remain in the cathode to sustain the high
charging voltage; in contrast, in a Li-ion battery, the Li.sup.+
depleted, transition metal oxide cathode is capable of holding the
voltage employed to charge the battery. The current and voltage
profiles from a Lithium-oxygen battery (La0430a.044) that was
subjected to charge-discharge cycling for four cycles using a
negative .DELTA.V charge termination are shown in FIG. 17. Sample
cathode has 14% of Li.sub.2O.sub.2 and was cycled in 1 M LiPF.sub.6
in PC:DME (1:2 by wt.) with 2% Vinylene carbonate additive. The
spikes in the third cycle is due to power disruption. Cycle
capacity of the cell is plotted as a function of cycle number in
FIG. 18.
[0049] Remarkably, the charging profiles, voltage and current, are
free of noise in the first four cycles. Based on impedance
characteristics of the cathode, charge termination may occur at
different voltages in different cycles; this issue is currently
under investigation. In general, with increase in the number of
cycles, due to an apparent increase in the cathode impedance, the
charge termination occurs at higher voltages, or the charging
voltage reaches the limit set by the algorithm (4.7 V in the above
example), and undergoes charging at constant voltage until current
is reduced to specified cut off value.
[0050] Based on these tests, some basic conclusions may be
apparent: (1) Charging to higher voltages (>4.6 V) is necessary
to fully charge the cell by decomposing Li.sub.2O.sub.2. When cells
were charged to these higher voltages, the capacity fade in
discharge was minimized relative to the cases where the cells were
only charged to 4.3 V or less. (2) Cells need to be subjected to a
`formation` process to allow a slow charge initially. In fact, a
slow charge may be necessary in subsequent steps also, since
charging at higher rates (1 mA/cm.sup.2) seems to cause severe
noise in both current and voltage profiles. (3) Negative delta V
charging process is effective in reducing the noise in
voltage/current profiles which may related to the side effect in
Li/O.sub.2 batteries.
[0051] Feasibility of a rechargeable lithium/oxygen battery with no
lithium or oxygen in the original battery structure has been
investigated. Both lithium and oxygen will be released during the
initial charging process from Li.sub.2O.sub.2 pre-mixed in cathode.
Lithium anode will be deposited on copper current collector during
this formation process. If feasible, this rechargeable
lithium/oxygen battery will further improve the specific energy of
the Li/O.sub.2 battery. A Lithium metal-free Li/O.sub.2 battery was
prepared for use in blue bag cells.
[0052] In a rechargeable lithium/oxygen battery with no lithium,
nor oxygen in the original battery structure. Both lithium and
oxygen will be released during the initial charging process from
Li.sub.2O.sub.2 pre-mixed in cathode. This rechargeable
lithium/oxygen battery will be self-sustainable in a closed
environment; therefore the problems associated with lithium
corrosion when exposed to air/moisture can be eliminated.
[0053] Feasibility of a rechargeable lithium/oxygen battery with no
lithium or oxygen in the original battery structure has been
investigated. Both lithium and oxygen will be released during the
initial charging process from Li.sub.2O.sub.2 pre-mixed in cathode.
Lithium will be deposited on copper current collector during this
formation process (for the cells with a structure shown in FIG.
1(b)) or intercalate into graphite (or soft carbon) electrode (for
the cells with a structure shown in FIG. 1(c)).
[0054] A Lithium metal-free Li/O.sub.2 battery was prepared for use
in polymer/metal lamination bag. A plain copper foil, which is to
be used as the anode current collector, was laminated between two
identical cathode layers made of the initial carbon layers. The
results from tests are shown in FIG. 19. It shows that the Li-free
cells function quite well for the first a few cycles. The discharge
profiles show very good shapes, consistent with the battery
operation, and the impedance of the cells seems to be low.
[0055] Significant progress has been made during the last quarter,
on both the reversibility and discharge capacity of Li/O.sub.2
cells. A Li/O.sub.2 cell with a Li.sub.2O.sub.2 containing carbon
cathode and lithium metal anode have been cycled in 1 M LiPF.sub.6
in PC:DME (1:2) for more than 13 cycles with a capacity fade of
.about.5.4%/cycle. The scale up procedures for assembling large
pouch cells for Li/O.sub.2 batteries have been developed. The
feasibility of lithium-metal-free Li/O.sub.2 battery was also
investigated. Further development of this technology can lead to a
high capacity Li/O.sub.2 battery with significant reversibility
which is suitable for military applications.
[0056] It should be understood that a typical reversible cathode
contains .about.14% Li.sub.2O.sub.2, but the range from 0.5 to 50%
are feasible. The battery capacity increases with increasing
proportion of active carbon and porosity. Suitable cathode active
material include: Calgon carbon (activated carbon), carbon black,
metal powders such as Ni, activated carbon cloths, porous carbon
fiber papers, metal foams. Suitable anodes includes: lithium metal,
lithium metal based alloys (Li--Al, Li--Sn, Li--Si etc.), other
lithium intercalating compounds used in Li-ion batteries such as
graphite, MCMB carbon, soft carbon, Lithium titanate, etc. A cyclic
voltammetry peak at .about.4.6 V is associated with decomposition
of Li.sub.2O.sub.2. Charge to more then 4.6V will enhance the
decomposition of Li.sub.2O.sub.2 Suitable Voltage range: 4 to 4.8 V
for charging; 3-1.5 V for discharging. Increasing cycling voltage
significantly increases the reversibility of the battery. PC based
electrolyte (1 M LiPF.sub.6 in PC:DME (1:2 in weight)) is the
preferred electrolyte for rechargeable Li/O.sub.2 batteries which
can be charged to more than 4.3 V. Other suitable electrolyte
include: 1 M LiPF6 in PC:THF (1:1), Other common electrolytes used
for Li ion batteries consisting of the following solvents based on
carbonates, esters, ethers, sulfones: Propylene carbonate, Ethylene
carbonate, Dimethyl carbonate, Diethyl carbonate, Ethyl methyl
carbonate, gamma-butyrolactone, sulfolane, 1,3-dioxolane,
Tetrahydrofuran, Dimethoxyethane, Diglyme, Tetraglyme, Diethyl
ether, 2-methyl tetrahydrofuran, tetrahydropyran, pyridine,
N-methyl pyrrolidone, dimethyl sulfone, ethyl methyl sulfone, ethyl
acetate, dimethyl formamide, dimethyl sulfoxide, acetonitrile,
methyl formate. Electrolytes, for both the cathode and the
separator, may be of the following lithium salts: LiPF6, LiBF4,
LiAsF6, LiClO4, LIBOB, LiTFSI, LiTriflate, LiBr, and LiI, i.e.,
(lithium hexafluorophosphate, lithium tetrafluoroborate, lithium
hexafluoroarsenate, lithium perchlorate, lithium
bis(trifluorosulfonyl) imide, lithium triflate, lithium
bis(oxalato) borate, lithium tris(pentafluoroethyl)
trifluorophosphate, Lithium bromide, and lithium iodide).
Preferably, the electrolyte contains a lithium intercalation
compound. An alkylene carbonate, such as vinylene carbonate
(Vinylene carbonate) or a butylene carbonate additive can improve
the high voltage stability of electrolyte. Suitable Vinylene
carbonate additive range: 0 to 10%. Suitable binders for carbon
electrodes: Kynar, PTFE, Teflon AF, FEP etc. Suitable operating
pressure: 0.5 to 100 Atm. Suitable operating pressure is between
0.5 to 100 Atm. It should be noted that a slow "formation" process
and a "negative .DELTA.V" charging process can increase the
stability of the cell.
[0057] It should be understood that the term "air" as used herein
is not intended to be limited to ambient air, and may include other
combinations of gases containing oxygen or an amount of pure oxygen
gas. This broad definition of the word "air" applies to all uses
herein, including but not limited to air battery, air cathode, and
air supply. It should be understood that the just described
invention may include a battery that has not formed the anode yet,
or include a battery which includes a preformed anode. When the
battery does not yet include an anode, the anode is formed upon
initial charging of the battery.
[0058] It thus is seen that a lithium-air battery is now provided
that is manufactured in an simply process. It should of course be
understood that many modifications may be made to the specific
preferred embodiment described herein, in addition to those
specifically recited herein, without departure from the spirit and
scope of the invention as set forth in the following claims.
* * * * *